Precipitates and
Solubility
Unit 8 – Solutions
Chapter 10, section 3
Precipitates & Solubility

Precipitates are insoluble products that occur
as the result of an ionic reaction.

Happens when two soluble ionic compounds
undergo a double replacement reaction.
—This means that the cations switch partners.
NaCl + KBr  NaBr + KCl

If one of the new products formed is insoluble in
water, it precipitates out.
AgNO3 + NaCl  NaNO3 + AgCl(s)
Precipitate
Here are the SOLUBILITY RULES
1. All nitrate (Things bonded with NO3-) salts are
soluble.
2. All salts containing the alkali metal ions (Li+,
Na+, and K+) and the ammonium ion (NH4+) are
soluble.
3.
Most chloride, bromide, and iodide salts are
soluble;
**Silver (Ag+), Lead (Pb2+), and Mercury
(Hg22+) are exceptions.
4. Most sulfates (Things bonded with SO42-) are
soluble *** Calcium (Ca+2), Barium (Ba+2),
Lead (Pb+2), and Mercury (Hg2+2) and Strontium
(Sr+2) are exceptions.
5. All Acetate (C2H3O2-) salts are soluble, **except
when bonded with iron (Fe+3)
6. Most hydroxide salts (Things bonded with OH -)
are insoluble.
7. All sulfide (S2-), carbonate (CO32-), chromate
(CrO42-), and phosphate (PO43-) salts are insoluble.
8.
Rules 1-5 override rules 6-7.
For example, this means that anything bonded to
an alkali metal like sodium, or bonded to
ammonium ion (NH4+) is soluble
These rules help you before and after a
reaction to figure out what will
happen.

If something will not dissolve in water,
then it won’t react with anything in the
water.

If a solution forms a precipitate, then you
can determine what that precipitate is just
by using these rules.
Example: AgNO3 + NaCl  Forms what?
First check if these two things dissolve at all.
Rules 1 and 3 say they do, so they do.
 You can use (aq) , which means aqueous, in the
reaction equation to show that it is dissolved in
water. This means that the ionic compound has
separated into its ionic parts and is solvated by
water molecules.
 To find the products, just switch the partners of
the reactants around.
 AgNO3 (aq) + NaCl (aq) 
AgCl + NaNO3


Now check if any of the products form a
precipitate. According to Rule 3, AgCl is
insoluble and will form a precipitate. You
can then use (s) for solid next to AgCl to
indicate it is a precipitate.
AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
Writing Full Ionic equations

Full Ionic Equations show all soluble ionic
compounds as ions.
Ag+(aq) + NO3- (aq) + Na+(aq) + Cl-(aq)
 AgCl(s) + Na+(aq) + NO3-(aq)

Ions that appear on both sides of the equation
cancel out to leave the Net Ionic Equation.
Writing Net Ionic Equations

The equation only includes the ions and
compounds that form a precipitate in the
reaction
Ag+ (aq) + Cl-(aq)  AgCl (s)
Spectator Ions – Those ions that remain
in solution after the reaction.
 Na+ and NO3- are the spectator ions for
the above reaction.
